1. Field of the Invention
The present invention relates to an apparatus for measuring wafer clamping tension, and more particularly, to an apparatus that can accurately measure and adjust the tension of an elastic member used in clamping the wafers, thereby preventing the clamped wafers from moving or dropping during a manufacturing process.
2. Description of the Related Art
In order to produce a highly-integrated, highly-functional semiconductor product, a variety of stringent operating conditions must be met during the intricate manufacturing process. Because of the minute dimensions and very small tolerances inherent in semiconductor manufacturing, one important requirement is the ability to firmly and accurately fix a plurality of wafers at predetermined positions while performing various semiconductor fabrication processes.
One conventional method of fixing wafers with an elastic member at a predetermined position is described in U.S. Pat. No. 5,350,427 (the ""427 patent), entitled xe2x80x9cWafer Retaining Platen Having Peripheral Clamp and Wafer Lifting Means.xe2x80x9d The ""427 patent describes a protruding fence at one end of a platen at which wafers are to be fixed, a finger assembly formed at the opposing end of the platen for applying pressure with an elastic member to push the edge of the wafer toward the fence, and an operational unit installed at a lower portion of the finger assembly for selectively operating the finger assembly to load/unload the wafers, so that the finger assembly and fence can prevent the wafers from moving or dropping during processing.
However, in semiconductor manufacturing facilities where wafers are clamped by employing such an elastic member, repeated use of the elastic member can change the tensioning characteristics thereof, which in turn can cause the elastic members to fail to apply the requisite pressure to push the wafer toward the fence. As a result, the wafers may drop or move from the predetermined position to thereby cause a problem in the manufacturing process.
In an effort to solve this problem, present methods use a common commercial tension gauge in an effort to estimate and measure the elastic force used for clamping wafers. However, a problem exists in that such methods do not produce consistent results because the workers that use the tension gauge may measure the tension at different positions and apply different pressures during the readings.
Accordingly, it is an object of the present invention to provide an apparatus for measuring wafer clamping tension that provides consistent and accurate results for elastic member tension, regardless of which worker initiates the measurement.
To achieve this and other objects, the present invention provides a wafer clamping tension measuring apparatus, including a base plate having a guide groove formed in an upper surface and a moving plate having a guide rail protruding from a lower surface and reciprocating with the guide groove. A tension gauge is fixed to an upper surface of the moving plate for measuring the tension of a wafer clamping elastic member confronting the tension gauge. A displacement restricting block is attached at one end of the base plate to restrict the movement of the moving plate relative to the base plate when the moving plate is displaced towards the displacement restricting block.
Preferably, the base plate includes protrusions extending from a lower surface. The protrusions may be oriented so as to be aligned with holes on a wafer pedestal pad on which the base plate is placed.
The tension gauge includes a tension rod extending from the tension gauge, and a tension measuring block fixed to the other end of the tension gauge, such that the tension measuring block contacts the wafer clamping elastic member. The height of the tension measuring block from the surface can be adjusted.
In another embodiment, the present invention provides a method for measuring a wafer clamping tension, wherein the base plate of the wafer clamping tension measuring apparatus is fixed relative to the wafer clamping elastic member, and then a moving plate that reciprocates relative to the base plate is pushed towards the wafer clamping elastic member. A tension gauge attached to the moving member measures and displays the tension value. Displacement of the moving plate is accurately determined and standardized through repeated procedures by a displacement restricting block attached to one end of the base plate.